For the manufacture of optical lenses, in particular optical lenses for spectacles, it is well-known in the art to manufacture such lenses from plastic material in order to achieve a low weight of the lenses, as compared with glass. Insofar, it is also known to either manufacture such plastic material lenses by mechanically working a lens blank or by molding or casting the lens from a polymerizable plastic material in its final shape.
U.S. Pat. No. 5,547,681 discloses a method and an apparatus for casting optical lenses. The apparatus comprises two molding shells of equal diameter being clamped in parallel orientation with respect to each other, wherein the clamping is effected by means of two jaws engaging the peripheral surfaces of the shells. At their inner surface the jaws are provided with sealings such that a hollow cavity is created being delimited on two parallel sides by the molding shells and at its periphery by the jaws. The molding shells on their interior surfaces are configured with the profile of the lens to be manufactured such that when the axial distance between the two molding shells is appropriately set, the hollow cavity has exactly the shape of the lens to be manufactured.
In another apparatus and a corresponding method, as disclosed in WO 01/32407 A1, mentioned at the outset, two molding shells are likewise utilized. The molding shells are arranged with a certain distance with respect to each other and are sealed at their periphery by means of a sealing element. In this prior art apparatus, however, the molding shells have a different diameter. The molding shell with the smaller diameter is tightly received in a tube-shaped sealing element. At its terminal end facing the larger molding shell, the sealing element terminates in a radially expanded flange. The larger molding shell is axially clamped or pressed against the radial surface configured by that flange under pressure. In this case, too, the hollow cavity is filled with a polymerizable plastic material.
In this case as well as in the case mentioned before, the plastic material is preferably polymerized by irradiating light thereon. For that purpose the molding shells are optically transparent for the corresponding wavelength (preferably ultraviolet light). Two sources of ultraviolet light are disposed on opposite sides of the molding shells, the light of which being irradiated into the hollow cavity for polymerizing the plastic material contained therein.
WO 01/32407 A1, further, discloses to utilize a circular shaped means for axially pressing or clamping the larger molding shell against the radial front surface of the sealing element. The circular shaped means is applied to the molding shell at its peripheral edge area with which the molding shell adjoins the radial front surface of the sealing element. Preferably, the clamping means shall be configured as a hood or as a multi-arm assembly. The clamping or pressing force for the clamping means shall preferably be generated by vacuum.
It is, therefore, an object underlying the present invention to improve an apparatus and a method of the type specified at the outset, such that an apparatus is achieved that may be operated reliably under practical conditions, and allowing on the one hand side to press or clamp the larger molding shell with the required high clamping pressure against the sealing element, and, on the other hand side, does not disturb the feeding of different molding shells for different lenses nor disturbs the approaching of lamps for polymerizing the plastic material mass.